Method and device for the decontamination of plastic flakes

ABSTRACT

A method for preparing contaminated plastics ground into flakes, such as RPET or such polymers, having at least decontamination and SSP treatment steps, with at least one reactor, with heating to the process temperature taking place essentially outside the reactor. Also, a device for carrying out the method, and having at least one decontamination reactor and at least one SSP reactor, a device for heating plastic flakes to the process temperature being arranged upstream of the decontamination reactor. Also an SSP reactor having at least two individual reactors, and preferably between 3 and 7 individual reactors.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority of InternationalPatent Application No. PCT/EP2006002356 filed on Mar. 15, 2006, whichapplication claims priority of German Patent Application No. 10 2005 013701.6 filed Mar. 24, 2005. The entire text of the priority applicationis incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to a method for preparing contaminated plasticsground into flakes, to a device for carrying out the method, and to areactor unit for carrying out an SSP (solid state polycondensation)treatment.

BACKGROUND

Consumer items made of plastic are used increasingly, for example,beverage bottles made of PET, household objects, such as, keys orsimilar items, or housing parts of electronic apparatuses. The worldwidespread of plastics in the greatest variety of fields has, in themeantime, reached such proportions that the raw materials are becomingrarer and thus more expensive. Recycling plastics is important not onlyfor environmental reasons, it is also becoming more advantageous from aneconomic standpoint.

As raw material prices increase, the recycling methods that are ofgreatest interest are those that either maintain or increase the qualityof the original material with regard to processability after recycling.

Originally, the assumption was that collected PET material (RPET), owingto the quality loss after recycling and different contaminations, couldno longer be used in the same application (for example, beveragebottles). However, it has recently become apparent that such a use ispossible. Methods exist which recycle the plastics at a qualitativelyhigh level, to allow their reuse in the same application (for example,the food sector).

Using a method according to DE 199 53 659 A1, post-consumer PET bottles(RPET) are crushed, and first washed and surface dried in the usual way.Then the flakes are introduced into a crystallizer, in which they areheated and crystallized by a hot gas stream at 180° C. Then, the flakesreach a shaft reactor, where they are recondensed continuously for atleast two hours in countercurrent flow with respect to an N2 gas stream(temperature approximately 220° C.). Then the flakes are cooled again inthis continuously running process. One drawback of this method is thatthe PET flakes are heated in the given reactors, i.e., in thecrystallizer and the shaft reactor, respectively, which requires arelatively large amount of heating energy. In addition, the heattransfer is carried out via (inert) gas, which requires a complicatedpreparation system for the heat transfer medium. Another disadvantage ofthe method is that the recondensation of the flakes is continuous. In acontinuous process management, the desired IV (intrinsic viscosity)cannot be set exactly, because the heating which can be carried out islimited by process parameters (for example, temperature and time). Thefact that the actual IV of the flakes to be treated can be different—forexample, some flakes have an intrinsic viscosity IV of 0.70 dL/g, whileothers already have a value of 0.76 dL/g—is not taken into account inthis procedure, so that all the flakes undergo an increase in theirintrinsic viscosity in the same way (same time, same processconditions), without taking into account their original IV.

Therefore, the problem of the present disclosure is to provide a methodand a device for recycling plastics, which present considerably reducedenergy consumption, and in which the IV of the plastics can be set in acontrolled manner.

SUMMARY OF THE DISCLOSURE

The disclosure is based on the realization that the contaminants are notdistributed evenly over the RPET, and that they are found primarily onthe surface, or in surface-near areas. Therefore, a decontaminationand/or SSP treatment are(is) sufficient to clean RPET so it becomessuitable for use with foods, and can be used again as packaging materialfor foods, for example, for beverage bottles. In addition, thedisclosure is based on the surprising realization that RPET, in contrastto new (virgin) PET, is not adhesive in the warn state, which, in thefirst place, allows for unproblematic processes in the processingtechnology (for example, the heating of RPET in a heating installation).The reason for this is that the RPET flakes contract in a surprisingmanner during the heating, which results in an increase of theirthickness or their characterizing length. At the same time, a structuredsurface is produced, which reduces the contact surface area between theflakes.

In principle, the size of the flakes plays no role insofar as thefeasibility of the method is concerned. The only factor that changeswith increasing particle size is the residence time in the reactors. Thelarger the average particle size is, the longer the residence time inthe reactor is as well. Therefore, it is also conceivable not to reducethe size of the plastic objects before their treatment, or to reduce itonly slightly. Thus, flakes are defined as any objects that, in theirshape and size, no longer correspond to their original application form.However, as a general rule, the flakes present an average particle sizeranging from a few millimeters to a few centimeters.

The prepping of the flakes before the preparation, i.e., the cleaningand the crushing, is usually carried out in larger collection centers;however, it is also conceivable to carry out the crushing and (coarse)cleaning of the flakes onsite, immediately before the preparation.

Preparation here denotes not only the surface cleaning ordecontamination of the flakes, but also the improvement orreconstitution of the physical and of the chemical properties of theflakes, to ensure a renewed high-value use (for example, in the stretchblow molding of beverage bottles), particularly for the packaging of,for example, liquid foods that come in direct contact with the plastic.

Because the method can be transposed to the large industrial scale andalso to small installations, the reactors are larger boilers,containers, etc., and also smaller containers, which can besubstantially closed off from the environment.

The heating of the flakes to be treated to the process temperature iscarried out according to the disclosure substantially in a treatmentunit, which is outside of the reactor. This heating can be either acontinuous heating or a batch-wise heating of the flakes. In the reactoritself, the flakes are barely heated, or no longer heated, but merelymaintained at a process temperature, or heat losses are compensated.Thus, the process control is substantially adiabatic.

SSP (solid state polycondensation) denotes the process of molecularchain elongation of plastics in the solid phase. The SSP process is astandard process, which every person skilled in the art of the field ofPET plastic technology knows. The term SSP treatment here can alsodenote a negative molecular chain elongation, that is adepolymerization, or a treatment in which the molecular chains onaverage remain substantially the same. Regardless of whether themolecular chains are shortened, lengthened, or remain the same, anadditional decontamination of the flake occurs during the SSP processdue to the process conditions (including temperature, time).

It is particularly advantageous to use a process control where bothdecontamination and the SSP treatment occur each in a separate reactor.The two reactors can thus be regulated independently of each other atthe same time with respect to their reaction conditions (pressure,temperature, gas type).

It is preferred for both reactors to be under adiabatic conditions. Itis conceivable for the small heat losses of the flakes to be compensatedin the reactor by a reactor heating. For this purpose, any heating typecan be used (for example, water, steam, electrical, heat carrier oil,such as, thermal oil).

According to a particularly preferred embodiment, the material to beprepared in the reactors is not set into motion, mechanically,pneumatically, or in any other way. As a result, during the process ofthe decontamination and the SSP treatment, respectively, the flakescannot become statically charged due to mutual friction or interactionwith the reactor walls, and also, no abrasion products build up, whichwould increase the difficulty or the complexity of continuing theprocess, or even make it impossible to carry out the process.

To remove the contaminants, a hot gas flows around the flakes during thedecontamination step. The hot gas is preferably air, to ensure that theprocess control is as simple as possible. In the decontaminationreactor, the temperature in the decontamination reactor here is 20-200°C., preferably 100-180° C., and most advantageously 150-170° C. Thefunctional capability of the process is ensured at all the indicatedtemperatures; only the residence time in the reactor changes. The higherthe temperature in the decontamination reactor is, the lower theresidence time is. The optimal operational point of the decontaminationreactor with respect to temperature is therefore 150-170° C., because,on the one hand, the temperature is relatively high and thus theresidence time in the reactor is relatively short, and, on the otherhand, air can be used as gas for removing the contaminants. Attemperatures above approximately 180° C., air can no longer be used ashot gas, because it would enter into different reactions with thematerial. In this case, one would have to use nitrogen, for example. Theprocess of the decontamination can also be carried out at a temperaturebelow 20° C.; however, the residence time in the reactor then becomesvery long. The gas has a temperature which corresponds substantially tothat of the decontamination process. As a result, heat losses of theflakes can be compensated.

With regard to heating the flakes to the process temperature, it ispossible to carry out the heating in a batch process or continuously. Itis preferred to carry out the heating continuously, as close as possibleto the decontamination reactor. The closer the heating unit is to thedecontamination reactor, the less abrasion products form during thetransport. The better the heat transfer from the heating unit to theflakes, the more energy can be saved in the heating process. To heat theflakes continuously before the decontamination, it is preferred to use aheating screw or a vibrating helical conveyor. Other heating units arealso conceivable, however, the heating screw and the vibrating helicalconveyor present the advantage of a good heat transfer to the flakes. Itis preferred to use thermal oil as the heat carrying medium in theheating screw, where, for example, the heating can also be carried outwith steam, with hot water, or electrically.

In a preferred embodiment, the SSP process is carried out atlow-pressure conditions. Although it is also possible to allow theprocess to take place under atmospheric conditions or excess pressureconditions, the vacuum offers the advantage that the substance transferof volatile compounds from the flakes to the gas phase is improved, andthus the contaminants can be removed better, and the conditions formolecular chain elongation are also more advantageous. The vacuum whichis used for the SSP process should optimally present a gas pressure ofat most 100 millibar, preferably 10-0.1 millibar. If the SSP process iscarried out under atmospheric conditions or excess pressure conditions,then one must ensure that there is sufficient flow around the particles,to improve the substance transfer, or to be able to remove thecontaminants better.

In a preferred embodiment, the temperatures in the SSP reactor foradjusting the IV are higher than in the decontamination reactor. Thetemperature here preferably has at least the value of the temperature inthe decontamination reactor, and at most the value of the meltingtemperature of the flakes to be treated. The temperature here isadvantageously 150-250° C., and particularly advantageously 170-210° C.

The increase the process temperature, from the temperature of thedecontamination reactor to that of the SSP reactor, is carried outpreferably in a separate heat transfer device located between the tworeactors. It is preferred for the heat transfer device to be again aheat exchanger, or a heating installation, which uses thermal oil as theheat transfer medium. According to a particularly preferred variant, theheat transferring device is a heating screw or a vibrating helicalconveyor. The use of a hot air conveyor, an infrared tunnel, or asimilar device is also conceivable.

Special advantages in carrying the SSP process can be achieved byconducting the process under an inert gas atmosphere. If nitrogen orcarbon dioxide is used as protective gas, the process can be carried outparticularly well. Additional advantages arise from the use of the gasstream which removes degradation products, contaminants, ultrafineparticles or similar substances from the reactor. The gas in which theSSP process occurs is preferably atmospheric gas. The gas stream here aswell is preferably not too strong, so that the gas flakes are not moved.The only purpose of the gas stream is to ensure the removal of thedegradation products.

To optimize the process with regard to the regulation of the IV of theflake, the current value of the intrinsic viscosity is determined atleast once during the preparation process. However, it is particularlypreferred to use the procedure in which the IV is measured at leasttwice, where the results of the measurements determine the furthercourse of the process, for example, the residence time or thetemperature course.

In this context, it is particularly preferred to use a method in whichthe IV is determined spatially and/or temporally before the entrance ofthe material to be prepared into the SSP reactor. Based on this value,with a fixed temperature, the residence time in the SSP reactor can bedetermined. After half of the calculated residence time has elapsed,another measurement of the IV is carried out, and based on this resultthe residence time remaining is controlled and corrected if necessary.The measurement of the IV of the flakes can be carried out either in thereactor or outside of the reactor, where the sample collection iscarried out by means of a flake sampling device.

However, it is also conceivable to use a method in which a measurementof the IV is carried out, and to use this result to establish thetemperature of the SSP process, the residence time being fixed. Afterhalf of the fixed residence time has elapsed, a measurement of the IVcan be carried out again, where, based on the results, the temperaturefor the process time is controlled and corrected if necessary. In thisvariant of the method, the IV can also be measured analogously to theabove embodiment, either inside or outside.

If the measurement of the intrinsic viscosity yields the desired resultalready before the SSP treatment, then the process is regulated so thatthe IV no longer changes. This can be done, for example, by anappropriate regulation of the humidity content of the flake, which, onaverage, compensates for molecular chain shortening by hydrolysis, andfor molecular chain elongation by polycondensation. As a result, theoverall value of the intrinsic viscosity remains the same.

If the measurement of the intrinsic viscosity before the SSP treatmentyields an excessively high IV, a “negative” SSP treatment, i.e., acontrolled depolymerization, is carried out, by an appropriateadjustment of the humidity content of the flakes so that molecular chainshortening by hydrolysis prevails over molecule elongation bypolycondensation. The result is a lower IV.

If the regulation of the IV in the SSP reactor is completed, then acooling of the flakes to a temperature of 50-100° C., or, in a preferredembodiment, to below 70° C., can be carried out. The cooling is carriedout preferably in a cooling screw, a vibrating helical conveyor, or in afluidized bed reactor, although other cooling devices can also beprovided. If the cooling is carried out by means of a cold gas stream,then it is preferred to use environmental air, which ensures that thecooling process is simple. During the cooling of the environmental air,one must ensure that the total cooling process does not last too longand, particularly, that the cooling in the temperature range from thereaction temperature to 150° C. occurs very rapidly, preferably withinone to three minutes. If cooling at this speed is impossible, aprotective gas, preferably nitrogen or carbon dioxide, can be used, inthe case of the gaseous cooling medium. The use of another coolingmedium, such as, for example, a cooling liquid is equally possible.

The device for carrying out the method according to the disclosurepresents at least two reactors, of which one is preferably adecontamination reactor and one an SSP reactor for the regulation of theIV. In the reactors, any desired plastic flakes can be prepared, but itis preferred to use PET flakes.

The device for heating the flakes, which is preferably a heating screwor a vibrating helical conveyor, is connected before the decontaminationreactor. The purpose of the heating installation is to heat the flakesto the process temperature, before they enter into the treatmentreactor. The heat transfer in the heat exchanger or in the heatinginstallation can be designed much more efficiently than the heattransfer during the heating of the flakes in the reactor itself.

According to a particularly preferred variant, the decontaminationreactor presents a conical shape, which broadens in the direction ofgravity. This reactor design has the advantage that the heated flakes,which tend to form bridges, are prevented from doing so. Furthermore, itis possible for the reactor to present a heating installation which,although it does not heat the flakes, maintains their temperature, andthus compensates for heat losses.

According to a variant of the disclosure, at least two decontaminationreactors are provided, which present preferably a gas through-flowdevice, to be able to remove the contaminants from the reactor. A gasthrough-flow device can also be provided for both reactors. As a resultof the arrangement of two reactors, it is possible, for example, totreat different flakes in different reactors. This can become necessary,for example, if both thinner “trunk flakes” or wall flakes, and alsothinner “neck flakes” of beverage bottles are to be processed. Becausethe flakes have different characteristic lengths, they are introducedinto two different reactors with different process parameters. Anadditional heating installation is provided between the decontaminationreactor and the SSP reactor.

During the operation of the decontamination reactor, the filling heightand the residence time of the flakes are preferably nearly constant. Inaddition, the operation of the reactor is preferably continuous, so thatat all times exactly as many flakes are supplied as are removed afterthe decontamination.

The SSP reactor as well presents preferably a gas through-flow devicewhich is capable of removing the contaminants. Because the temperaturein the SSP reactor is preferably 170-210° C., the gas through-flowdevice is an inert gas feed, preferably with nitrogen or carbon dioxide,because otherwise there is the risk that the components of air, at thesehigh temperatures, will initiate an oxidation process whose consequencesmay include an undesired yellow coloration of the product.

In a preferred embodiment, the SSP reactor presents a pump for thegeneration of the vacuum and a pump for the removal of the contaminants.According to a particularly preferred variant, only a pump is present,which ensures both the generation of the vacuum and the removal of thecontaminants in the gas stream.

A cooling unit, which lowers the temperature of the flakes from that ofthe SSP process to a temperature below the glass transition point, isconnected after the SSP reactor.

According to a particularly preferred embodiment of the disclosure, atleast two reactors, preferably 3-7 individual reactors, are available toensure a near continuous process for the SSP treatment. The arrangementwith several reactors allows the batch-wise (interruption-free) processof regulating the IV through different reactors, in such a way that thecooling device, which is connected after the SSP reactor unit, issupplied continuously with hot flakes from the individual reactors ofthe reactor unit.

The SSP reactor unit presents preferably a flake distributor whichsupplies the different individual reactors successively. The individualreactors of the SSP reactor unit are preferably arranged in asubstantially circular structure, to have as compact as possible aconstruction.

In spite of the fact that the SSP process is run in the batch mode, thismultipart reactor arrangement can achieve a nearly continuous process.In this way, the advantages of a continuously running overall process(for example, the heating and cooling devices can be operatedcontinuously) can be combined with the advantages of the batch-wise SSPprocess (for example, the IV can be regulated more precisely as a resultof the batch-wise processing).

According to a second embodiment, there are both at least twodecontamination reactors and also at least two SSP reactors.

The treatment times in the decontamination reactor and in the SSPreactor are a function of the initial IV and of the characteristiclength, or of the particle size, of the flakes. They fall in the rangefrom 20 min to 5 hours, preferably 45 min to 2 hours, and particularlyadvantageously 1 to 1.5 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the device and of the method, respectively, isexplained in further detail with reference to the drawing. In thedrawing:

FIG. 1 shows a schematic representation of a process flowchart, and

FIG. 2 shows a schematic representation of a top view of an SSP reactorunit.

DETAILED DESCRIPTION

In FIG. 1, a flake metering device 1 is shown, by means of which theflakes are conveyed in a predetermined manner into the decontaminationheating screw 2. During the addition into the flake metering device 1,the flakes are washed, and their residual humidity is less than 3%. Atthe beginning of the transport of the flakes through the decontaminationheating screw 2, they are at room temperature T1. (Flakes from previousprocesses may also still retain residual heat.) During the transportthrough the decontamination heating screw 2, which is operated withthermal oil, the temperature increases from room temperature T1 to theprocess temperature T2, where the process temperature is 150° C. Theflakes here crystallize sufficiently so that they can be transportedwithout problem and are not sticky.

After heating the flakes to the process temperature, they are introducedinto the decontamination reactor 3, which presents a conical shapebroadening in the direction of gravity. There, the decontamination ofthe flakes starts immediately. Once the filling height in thedecontamination reactor 3 is reached, the flakes continue to betransported at the same rate through the flake metering device 4 intothe SSP heating screw 5, where they are moved from the decontaminationheating screw 2 into the decontamination reactor 3. As a result, thefilling level in this continuous operating procedure always remains atan optimal level. The process is regulated here in such a way that theresidence time of the flake in the decontamination reactor 3 can nolonger fall below the minimum residence time.

The temperature T3 in the decontamination reactor 3 is 150° C. Thecrystallization or decontamination of the flakes is carried out as afunction of the two factors, time and temperature. The air feed, bymeans of which the contaminants expelled from the flakes are removed, isa supporting characteristic of this process. The air is heated to theprocess temperature T3, and introduced by means of the air feed 11 intothe decontamination reactor 3, it flows through the flakes located inthe decontamination reactor 3, and it is moved out by means of the airremoval device 12. The flow rate of the air must not fall below aminimum value, and in the process it is set so that the flakes do notbecome turbulent. The only purpose of the air stream is to remove thecontaminants expelled from the flakes more easily and more rapidly. Theair presents substantially a temperature in the range of the processtemperature. In the decontamination reactor 3, no heating of the flakesthus occurs, but only a stabilization of the temperature at the processtemperature.

Because the transfer of the flakes from the decontamination reactor 3into the flake metering device 4 and into the SSP heating screw 5 isoptimally insulated, and thus there is no heat loss, or as little heatloss as possible, the flakes present a temperature T4 of 150° C. at thebeginning of the SSP heating screw 5 which conveys the flakes into theSSP reactor 6. In the SSP heating screw 5, which is operated withthermal oil, the flakes are heated from 150° C. (T4) to 190° C. (T5).

To optimize the process control with regard to the IV of the flakes, theintrinsic viscosity of the flakes is determined automatically by an IVmeasurement device 14 which is located on the SSP reactor, after orduring the filling process. Using this measurement value, the residencetime of the flakes in the SSP reactor 6 is determined.

To facilitate the further removal of contaminants and the increase ofthe intrinsic viscosity, a vacuum is applied to the SSP reactor 6, whichis substantially cylindrical in shape, with a gas pressure of 1 millibarusing a vacuum pump 9. To improve the removal of the contaminants,nitrogen or carbon dioxide is supplied through an inert gas inlet 15,and it flows around the flakes in such a way that they do not becometurbulent. The inert gas enriched with contaminant is removed by suctionthrough the vacuum pump 9. The temperature T6 in the SSP reactor 6 is190° C.

After half of the originally calculated residence time of the flakes inthe SSP reactor 6 has elapsed, a sample of the flake is analyzed againwith the IV measurement device 14 to determine the value of theintrinsic viscosity. Due to the changes in the IV of the flake, theremaining residence time in the SSP reactor 6 can be controlled orcorrected. Based on the two measurements of the IV during the SSPtreatment, an optimal process result with regard to intrinsic viscositycan be achieved.

After the treatment in the SSP reactor 6, the flakes are introduced intoa flake metering device 7, from which they are fed by metering into thecooling reactor 8. In the flake metering device 7, the flakes present atemperature T7 of approximately 190° C., which is the temperature of theSSP process. The cooling of the flakes in the cooling reactor 8 to atemperature T8 of approximately 70° C. is carried out by means ofenvironmental air. The cooling must occur so rapidly that, in spite ofthe humidity contained in the environmental air, no hydrolysis of theflakes takes place.

FIG. 2 shows a special design of the SSP reactor 6. Here five,substantially cylindrically, individual SSP reactors 61, 62, 63, 64 and65 are arranged in a circular structure to form an overall SSP reactor6. After heating the flakes from T4 to T5 (150° C. to 190° C.) in theSSP heating screw 5, they are distributed in a controlled manner intothe individual reactors through a distribution funnel 16 anddistribution ducts 13.

The flakes are directed, for example, by the distribution funnel 16through a distribution duct 13 into the individual SSP reactor 61 untilthe latter has reached the process filling height. While, in theindividual SSP reactor 61, the SSP process starts with the measurementof the IV by the IV measurement device 14, the flakes which continue tobe continuously conveyed by the SSP heating screw are led through thedistribution funnel 16 and the distribution duct 13 into the individualSSP reactor 62, until the production filling height is reached. Whilethe SSP process in the individual SSP reactor 62 now starts with ameasurement of the IV of the flakes, the individual SSP reactor 63 isfilled with heated flakes. In this way, the individual SSP reactors61-65 are filled successively with flakes.

Until the individual SSP reactor 65 is filled with flakes, the SSPprocess in the individual SSP reactor 61 is completed, and the flakesare removed through the flake metering device 7 in the direction towardsthe cooling reactor 8. Therefore, the individual SSP reactor 61 can alsobe filled again after the individual SSP reactor 65 has been filled. Inthis way, the SSP process, which is preferably carried out batch-wise,can be run as a nearly continuous process with continuous flake feedfrom the SSP heating screw 5 and with continuous flake removal by theflake metering device 7 into the cooling reactor 8.

1. A method for preparing plastics that are contaminated and ground intoflakes, comprising at least a decontamination step and a SSP treatmentstep performed on the flakes, each taking place in at least one reactorand the SSP treatment being adiabatic, wherein the decontamination ofthe flakes is carried out in at least one decontamination reactor andthe SSP treatment of the flakes is carried out in at least one SSPreactor, wherein a SSP process temperature of the flakes in the SSPreactor is higher than a decontamination process temperature of theflakes in the decontamination reactor, and wherein heating the flakes tothe SSP process temperature occurs while the flakes are located outsideof the SSP reactor.
 2. The method according to claim 1, and wherein nomechanical energy is added to the material to be prepared in the SSPreactor.
 3. The method according to claim 1 further comprising a hot gasthat flows around the material to be prepared in the decontaminationreactor.
 4. The method according to claim 3, wherein the hot gas thatflows around the material to be prepared is air.
 5. The method accordingto claim 1, wherein the decontamination of the flakes takes placecontinuously in the decontamination reactor.
 6. The method according toclaim 1, wherein, in the decontamination reactor, the temperature is inthe range from approximately 20° to 200° C.
 7. The method according toclaim 1, wherein the heating of the material to be prepared to thedecontamination process temperature occurs continuously before thedecontamination reactor.
 8. The method according to claim 7, wherein theheating occurs in one of a heating screw or in a vibrating helicalconveyor.
 9. The method according to claim 8, wherein thermal oil isused as medium for transferring heat to the material to be prepared. 10.The method according to claim 1, wherein the SSP treatment in the SSPreactor is carried out in batches.
 11. The method according to claim 1,wherein low pressure conditions exist in the SSP reactor.
 12. The methodaccording to claim 11, wherein, in the SSP reactor, a vacuum is presentwith a gas pressure of at most 100 mbar.
 13. The method according toclaim 1, and wherein the SSP process temperature is in the range fromapproximately 150° to 250° C.
 14. The method according to claim 1,wherein the temperature increase of the material to the SSP processtemperature occurs continuously before the entry into the SSP reactor.15. The method according to claim 14, wherein the temperature increaseto the SSP process temperature occurs in one of a heating screw or in avibrating helical conveyor.
 16. The method according to claim 14,wherein thermal oil is used as medium for transferring heat to thematerial to be prepared.
 17. The method according to claim 1, whereinthe SSP process is carried out under a protective gas atmosphere. 18.The method according to claim 1, wherein a gas stream is led through thematerial to be prepared, which removes at least one of degradationproducts, contaminants, and ultrafine particles from the SSP reactor.19. The method according to claim 1, wherein the IV of the material tobe prepared is determined at least once before or during the preparationprocess.
 20. The method according to claim 19, wherein the result of theIV determination determines at least parts of the process course. 21.The method according to claim 1, and carrying out a measurement of theIV before the entry of the material to be prepared into the SSP reactor,and, based on its results, determining a residence time of the materialin the reactor.
 22. The method according to claim 20, further comprisingcarrying out an additional measurement of the IV after substantiallyhalf of the determined residence time of the material to be prepared inthe SSP reactor, and, based on the results thereof, controlling thepreviously determined residence time in the SSP reactor.
 23. The methodaccording to claim 1, further comprising cooling the material to beprepared, after the residence time in the SSP reactor, to a temperaturebelow the glass transition point.
 24. The method according to claim 23,wherein the cooling is carried out in one of a cooling screw, avibrating helical conveyor, or in a fluidized bed reactor.
 25. Themethod according to claim 23, wherein the cooling is carried out bymeans of environmental air.
 26. The methoding according to claim 1,wherein the contaminated plastics ground into flakes comprisepost-consumer plastics.
 27. The methoding according to claim 1, whereinthe contaminated plastics ground into flakes comprise RPET.
 28. Themethoding according to claim 1, wherein the IV of the material to beprepared is determined at least once before or during the preparationprocess.
 29. A method for preparing plastic flakes, the methodcomprising: heating the plastic flakes to a first process temperatureprior to delivering the plastic flakes to a decontamination reactor;decontaminating the plastic flakes in the decontamination reactorwithout heating the flakes beyond the first process temperature; heatingthe plastic flakes to a second process temperature at a location outsideof the decontamination reactor after decontaminating the plastic flakesin the decontamination reactor and prior to delivering the plasticflakes to an SSP reactor, the second process temperature greater thanthe first process temperature; and decontaminating the plastic flakes inthe SSP reactor without heating the plastic flakes beyond the secondprocess temperature.